CONO-SUR 2009 Problem 4
Andrea and Bruno play a game on a table with rows and columns. First Andrea divides the table in zones. Each zone is formed by contiguous cells aligned vertically or horizontally, as shown in the figure.
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Then, Bruno writes one of the numbers in each cell in such a way that the sum of the numbers in each zone is equal to . Bruno wins if the sum of the numbers written in each of the columns of the table is a prime number. Otherwise, Andrea wins. Show that Bruno always has a winning strategy.
Dataset text AI-MO AoPS. Quoted with source.
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